Objects to be weighed, such as detergents and confectionery, which have been weighed to have specified weight by a combination weigher, are typically packaged by a packaging machine. A schematic construction of a first conventional example of such a combination weigher which weighs the objects to be weighed is shown in FIG. 12.
The combination weigher of FIG. 12 is configured such that a control unit 30 controls an operation of the entire combination weigher and performs combination calculation. The combination weigher is constructed in such a manner that a center base body (body) 5 is disposed at a center of the combination weigher, and a dispersion feeder 1 having a conical shape is mounted to an upper part of the center base body (body) 5 to radially disperse objects to be weighed supplied from an external supplying device by vibration. Around the dispersion feeder 1, linear feeders 2 are provided to transfer the objects to be weighed which have been sent from the dispersion feeder 1 into respective feeding hoppers 3 by vibration. A plurality of feeding hoppers 3 and weighing hoppers 4 are disposed below the linear feeders 2 and are arranged in a circular shape in such a manner that each feeding hopper 3 and each weighing hopper 4 correspond to the associated one of the linear feeders 2. The feeding hopper 3 receives the objects to be weighed which have been sent from the linear feeder 2, and opens its gate to feed the objects to be weighed to the weighing hopper 4 located therebelow when the weighing hopper 4 becomes empty. The weighing hopper 4 is attached with a weight sensor 41 such as a load cell. The weight sensor 41 measures the weight of the objects to be weighed inside the weighing hopper 4. The control unit 30 performs combination calculation to select a combination made up of hoppers which will discharge the objects to be weighed, from the plurality of weighing hoppers 4. The weighing hoppers 4 corresponding to the combination discharge the objects to be weighed onto a collecting chute 6. The collecting chute 6 is disposed below the weighing hoppers 4. The objects to be weighed which have been discharged from the weighing hoppers 4 slide down on the collecting chute 6 and are discharged from a discharge outlet at a bottom part of the collecting chute 6. The objects to be weighed are sent out to a packaging machine which is not shown. While manufacturing package bags, the packaging machine charges the objects to be weighed which have been discharged from the combination weigher into the package bags and packages them.
In order to increase a productivity (total number of times the objects to be weighed are discharged from the combination weigher to the packaging machine) within a specified time, it is necessary to shorten a discharge cycle time. To this end, conventionally, the number of weighing hoppers was increased to a certain degree to configure so that a double shift operation is carried out rather than a single shift operation, and thus the discharge cycle time taken for the single shift operation is reduced by half. The single shift operation is carried out in a configuration in which, for example, a total number of the weighing hoppers 4 is set to ten, the number of the weighing hoppers 4 selected to make up of a combination is set to four, the combination calculation is performed once within one weighing cycle time, the weighing hoppers 4 perform discharge operation once within one weighing cycle time, and the collecting hopper 7 performs discharge operation with respect to the packaging machine once within one weighing cycle time. In order to achieve weighing precision substantially as high as that in the single shift operation when the double shift operation is carried out, the number of the weighing hoppers 4 is increased by four so that a total number of them is fourteen and the number of the weighing hoppers 4 to be selected to make up of the combination is set to four. And, the combination calculation is performed once in every ½ of one weighing cycle time, and weighing hoppers 4 making up of a combination selected in the combination calculation discharge the objects to be weighed. In this case, since the combination calculation is performed twice within one weighing cycle time, and the weighing hoppers 4 performs the discharge operation twice within one weighing cycle time, high-speed discharge operation is achieved, and the productivity is improved.
However, even when the combination weigher shown in FIG. 12 is configured to carry out the double shift operation, the speed of the objects to be weighed which have been discharged from the weighing hoppers 4 and slide down on the collecting chute 6 does not increase. For this reason, on the collecting chute, a distance between a batch of the objects to be weighed discharged from the weighing hoppers 4 selected to make up of a previous combination and a batch of the objects to be weighed discharged from the weighing hoppers 4 selected to make up of a subsequent combination is insufficient and the objects to be weighed in the previous and subsequent combinations are likely to be mixed, making it difficult to carry out the high-speed discharge operation. To solve this problem, two collecting chutes may be provided as shown in FIG. 13.
FIG. 13(a) is a schematic partial cross-sectional view showing a second example of the conventional combination weigher as viewed from laterally. FIG. 13(b) is a schematic view of collecting chutes (inner chute and outer chute) and weighing hoppers of the combination weigher as viewed from above. The combination weigher is configured in such a manner that a lower chute is incorporated into the combination weigher (such as the combination weigher disclosed in Japanese Laid Open Application No. Sho. 57- 125322) to discharge objects to be weighed into a packaging machine having one inlet.
In the combination weigher, two collecting chutes, i.e., an inner chute 6g and an outer chute 6h are provided, and each weighing hopper 4 has two gates (not shown) to be able to discharge objects to be weighed selectively to the inner chute 6g or to the outer chute 6h which is located therebelow. In addition, a collecting hopper 7g is provided at a discharge outlet 6ge provided at a bottom part of the inner chute 6g to hold and discharge the objects to be weighed, while a collecting hopper 7h is provided at a discharge outlet 6he at a bottom part of the outer chute 6h to hold and discharge the objects to be weighed. Furthermore, one lower chute 8 is provided below the two collecting hoppers 7g and 7h to feed the objects to be weighed which have been discharged from the collecting hoppers 7g and 7h into one inlet of the packaging machine. A control unit 31 controls an operation of the entire combination weigher and performs combination calculation. The combination weigher is configured to carry out the double shift operation in such a manner that the weighing hoppers 4 selected sequentially to make up of the combinations discharge the objects to be weighed alternately to the inner chute 6g and to the outer chute 6h and the collecting hopper 7g and the collecting hopper 7h alternately discharge the objects to be weighed to the lower chute 8. Thereby, the objects to be weighed are discharged twice from the discharge outlet 8a of the lower chute 8 within one weighing cycle time. So, the high-speed operation is achieved. Also, since the weighing hoppers 4 discharge the objects to be weighed to each of the inner chute 6g and the outer chute 6h only once within one weighing cycle time, a sufficient distance can be provided between a batch of the objects to be weighed which are discharged previously and a batch of the objects to be weighed which are discharged subsequently on each of the chutes.
In cases where the combination weigher is not equipped with the lower chute 8, two packaging machines or a twin-inlet packaging machine having two inlets are/is disposed below the combination weigher, and the objects to be weighed which have been discharged from the collecting hoppers 7g and 7h are fed into the associated packaging machine inlets. In this case, by the double shift operation, the objects to be weighed are discharged once to each of the two packaging machine inlets within one weighing cycle time. That is, the objects to be weighed are discharged twice in total within one weighing cycle time irrespective of the presence or absence of the lower chute 8. Thus, productivity within a specified time period can be improved.
Japanese Examined Patent Application Publication No. Hei. 8-125322 discloses a configuration of a combination weigher which is capable of carrying out a combination discharge operation at a higher speed. In this configuration, a funnel-shaped inner chute is disposed below weighing hoppers and right and left outer chutes are disposed to surround the inner chute. Intermediate hoppers are respectively provided at discharge outlets at bottom parts of these three chutes. Furthermore, three first timing hoppers are disposed below the three intermediate hoppers to discharge the objects to be weighed to a first lower chute and three second timing hoppers are disposed below the three intermediate hoppers to discharge the objects to be weighed to a second lower chute. The objects to be weighed can be fed from the first and second lower chutes to the two packaging machines or the twin-inlet packaging machine. In this case, a combination for discharging the objects to be weighed to the right outer chute is determined by selecting weighing hoppers from those belonging to a right group, a combination for discharging the objects to be weighed to the left outer chute is determined by selecting weighing hoppers from those belonging to a left group, and a combination for discharging the objects to be weighed to the inner chute is selected from the remaining weighing hoppers. The weighing hoppers selected to make up of these three combinations discharge the objects to be weighed simultaneously, and the intermediate hoppers provided at the discharge outlets of the three chutes hold the objects to be weighed. Holding the objects to be weighed, each of the intermediate hoppers discharges the objects to be weighed alternately to the associated one of the three first timing hoppers and to the associated one of the three second timing hoppers. The three first timing hoppers sequentially discharge the objects to be weighed to the first lower chute, while the three second timing hoppers sequentially discharge the objects to be weighed to the second lower chute.